Signal processing, as used in such technical areas as character recognition, data transmission and spectral analysis, requires that very large numbers of data elements be processed within short time intervals. It is not feasible to do so in real time using a conventional computer. Formerly, signal processing was carried out by specialized analog and digital circuits tailored to specific applications. The first digital systems to be marketed for signal processing purposes took the form of relatively inexpensive microprocessors.
French Pat. No. 74 43561 (publication No. 2,296,221) describes a modular signal processing system relying upon a master-slave relationship. The basic system comprises a microprocessor used as a control unit and a specialized microprocessor used as a multiplier-accumulator. If the processing of the signal calls for a greater computing power, a second microprocessor serving as a multiplier-accumulator is added to the first.
In the fields of spectral analysis and high-speed data processing, signal processing essentially involves computing the products of convolutions and correlations of complex numbers (digital filtering, computation of discrete Fourier transforms), that is to say, the sums of products of two complex operands. This obviously calls for a very great computing power since in order merely to compute a product of two complex operands four multiplications must be performed, two of these being necessary to work out the real part of the product and the other two to determine the imaginary part thereof. These four multiplications might conceivably be performed sequentially, but this could hardly be done within the short time intervals allocated. They could be performed in parallel, but then provision would have to be made, in a system of the type described in the aforementioned patent, for at least two microprocessors that would be used as multiplier-accumulator devices in conjunction with an algorithm designed to assemble the real and imaginary parts of the results of the four multiplications.